yeah, I believe that bet will go unclaimed. For me - using different comb materials is basically because I know that the difference in tone is all in my head. Literally. So, for me a controlled test would not be possible to disclaim my personal belief.
Cham Ber Huang did quite a bit of research in the 60's, I believe. He and his brother worked feverishly trying to unlock the secrets of the comb material question too. There's lots to consider in comb design and material.
Ultimately, when controlled tests, or blindfold tests are done - it seems no person alive can tell the difference... but I reitterate, to me, I feel wood has a warmer sound than plastic, metals are brighter. The problem there is that I am not using controls. So, all the tonal effect to me is just in my head - and I am fine with that. =)